Preliminary Research Of Thermal Stress Of Shaft Lining

Since 1987, nearly 60 shaft wall fractures were taken place in Xu-Huai mining area. Many researches are done about the mechanism of shaft wall fractures. And, the past research shows that the vertical additional force due to the loss of bottom aquifer is the main factor that results in shaft wall fracture. On the other hand, more researches about thermal stress are done in many fields, but only few are reported about shaft wall structure. One report reveals that thermal stress is the main controlling factor for shaft wall fracture. Due to the above different opinions, the research of thermal stress about shaft wall structure is of significance in theory and in practice.Firstly, the calculation methods are summed up including gravitational stress, geostress and additional stress by the loss of bottom aquifer. Secondly, because the temperature field is the base to calculate thermal stress, Finite Differentiate Method is used to simulate temperature field of shaft lining and four kinds of thermal stress as well as their calculation methods are introduced. And then, take a given shaft lining in Xuzhou as an example, all the stresses are calculated including gravitational stress, geostress, additional stress due to the loss of water of bottom aquifer, and four kinds of thermal stress. Finally, the regulations of these four kinds of thermal stress are analyzed, and the proportions are calculated and discussed for each stress in the total vertical stress.The above work shows that: 1.The thawing settlement and vertical restraining thermal stress are main components of the total thermal stress, up to 99%. 2. Total vertical thermal stress of shaft lining increases with the increase of depth and reaches the maximum near the interface of bottom aquifer and bedrock. And, the value in summer (about 8.9Mpa) is more than it in winter (about 7.1Mpa). 3. The ratio of thermal stress in total stress decreases with the draw-down of bottom aquifer. In summer and at the interface of bottom aquifer and bedrock, the ratio of thermal stress in total vertical stress of shaft wall is about 37%, 19% when the loss of bottom aquifer is 5m, 35m. And conversely, the proportion of loss of bottom aquifer is about 13%, 55%.Based on the above research, two conclusions can be drawn as follows: l.With the increase of draw-down of bottom aquifer, the stress for the loss of bottom aquifer becomes main controlling factor affecting the stabilization of shaft lining. 2. Thermal stress is with a considerable part in total stress, so as to be an important factor. The thermal stress can't be neglected in the area of shaft lining.The conclusions above need to be further researched and tested due to the preliminary study. Due to the less research about thermal stress and the importance revealed in past work, suggestion is given to do more study so as to provide more reliable reference for design, construction and prevention.